In Antarctic lake, extreme conditions lead to extreme genetics

In a frigid, salty lake, microbes swap genes at an unprecedented rate.

Despite temperatures well below freezing, Antarctica's Deep Lake remains unfrozen thanks to its extremely high salt content. The lake was isolated from the oceans about 3,500 years ago, when the continent lifted up around it. As inhospitable territory goes, this is pretty high on the list, a lake both colder and more saline than most living things can survive.

The extremophiles that inhabit these waters belong to a group called haloarchaea, microbes that actually require high salt concentrations. A team of Australian and American scientists who set out to study the genetic diversity of the lake's microbes discovered that the haloarchaea have responded to their extreme environment with extremely high rates of genetic exchange with other species, even other genera. The microbes use horizontal gene transfer—passing sections of genetic code to one another—to rapidly adopt any changes that help them adapt to this harsh environment.

They found four distinct genera had adapted to life in the lake in different ways. Despite their overall genetic differences, these regions had been sharing a lot of DNA. Long regions appear to be swapped whole, a phenomenon never before observed in a natural environment, scientist Rick Cavicchioli, a professor at the University of New South Wales, said.

What surprised Cavicchioli and his colleagues was that despite this high rate of gene sharing, the lake maintained distinct species instead of evolving into one homogenous ecosystem with a single dominant species. Ecologically, the species had developed different niches, using different food sources and different parts of the lake habitat.

The lake is so cold that it's the most unproductive lake in the world—very little energy is available for the haloarchaea, so they metabolize and reproduce very slowly compared to their relatives in other environments. One of the Deep Lake species produces about six generations a year. That's about 100-fold less than haloarchaea species observed in acidic environments created by mine drainage, for example.

The high level of gene sharing might be an adaptation to maintain diversity under slow reproductive conditions (though all haloarchaea swap DNA to some degree). "This is the only cold hypersaline system that has been studied, so we don’t know about others," Cavicchioli said in an e-mail. "On my coming expedition (leaving in a few weeks) we will take samples from other lakes that might have similar communities."

Understanding how haloarchaea are able to survive and thrive under the extreme salt and cold could have practical applications, Cacicchoil said. Their enzymes could conceivably be put to work cleaning up hazardous waste at sites in cold climate or put to use in temperature-sensitive industrial processes.

I wish I could swap genes like that. I can think of a few I'd love to replace: hairline, baseline metabolism, family history of diabetes and HBP, Crohn's disease. But, hey, at least I have a nice smile.

Which came first: the “haloarchea” label, or the adaptations? That is, were the bacteria already pretty well-adapted to high-salt waters, then became more so, or were they ordinary bacteria that somewhat uniquely took on dramatic adaptations, both vertically and horizontally?

The really tantalizing idea here is that dramatic, vastly-different mechanisms could evolve in such a metabolically-downclocked environment.

Thanks Wheels, I was gonna point that out. I was in college biology when this group was first established as a new domain. The micro-bi staff was going nuts over this news. To quote the resident nerd in Spielberg's classic "... uh, ... Life finds a way."

Which came first: the “haloarchea” label, or the adaptations? That is, were the bacteria already pretty well-adapted to high-salt waters, then became more so, or were they ordinary bacteria that somewhat uniquely took on dramatic adaptations, both vertically and horizontally?

Halobacteria are pretty widespread. If you've ever flown over salt flats (like in the south of San Francisco Bay) and noticed a reddish brown color, they're the reason. So, these were probably in the ecosystem when it got cut off, and were best able to deal with its increasing salinity.

I'm wondering what these “haloarchea” use as a food source. A land-locked lake in Antarctica can't have much by way of biological input, no rivers bringing leaves, branches and dead critters downstream, there can't be anything we'd normally consider a food source.

But they seem to require organic matter, and there appears no source for this.

The other source is carbon fixation, which seems the only option.

-- Other archaea use CO2 in the atmosphere as a source of carbon, in a process called-- carbon fixation (they are autotrophs). This process involves either a highly modified form-- of the Calvin cycle[97] or a recently discovered metabolic pathway called the -- 3-hydroxypropionate/4-hydroxybutyrate cycle.[98] The Crenarchaeota also use the-- reverse Krebs cycle while the Euryarchaeota also use the reductive acetyl-CoA pathway.-- [99] Carbon–fixation is powered by inorganic energy sources. No known archaea carry out-- photosynthesis.[100] Archaeal energy sources are extremely diverse, and range from the-- oxidation of ammonia by the Nitrosopumilales[101][102] to the oxidation of hydrogen-- sulfide or elemental sulfur by species of Sulfolobus, using either oxygen or metal ions-- as electron acceptors.

Does this suggest a lower level of the minimum amount of energy required for life to exist -- or does it confirm anything we thought we knew about the lowest practical level?

I mean, I figure you need enough energy to support n-number of generations -- an ecosystem that could only reproduce incredibly slowly would only survive so long as nothing disturbed it. Any shock to the system could kill the organism if it slowed or disturbed the reproductive rate.

Or is this a scenario where an organism could theoretically live for thousands of years, reproduce only every century or so, and might take many human lifetimes to even show signs of dying?

I'm a bit confused on trying to find any more details online about this "Deep Lake" in Antarctica. Is that the name of it (which it shares with many other lakes), or is there another name? Where is it in Antarctica? What are these extremes the article talks about?

If only humanity was willing to live more cooperatively with each other, working toward a mutually beneficial future.

A guy can dream, can't he?

I don't think so, no, you don't want that happen to our human species. Think deeper and you would realized what those microbes have been doing down there for so long at that extreme temperatures environment. They are having lots of fun, alright. To swap genes among each other, these microbes must involving group sex. They are most likely are not royally to a single sex-partner.

Now that says, when we are the most intelligent species among all, we properly do worse than these microbes when placed ourselves in such isolated environments. "Fun" is the word for many.

Lots of scientists say that if life can exist in extreme conditions then it must also exist on other planets with extreme conditions. I'm not sure about that. There is a key word in this text. Life ADAPTED. I'm pretty sure that once life is there at one moment, it will adapt to more extreme conditions, but it cannot be created in extreme conditions. We now know that there is life in places like that, but we have to prove how it can be created before assuming it can exist on other planets different than ours.

I always wonder if horizontal gene transfer is what made the genetic code universal. Any species that would have moved away from the standard code (and there are some rare examples) would have lost access to that "app store" of genetic diversity. Still, it is amazing that the microbial community in the saline, cold lake is showing such a high degree of DNA transformation. I wonder whether the salt and and the low temperature make those cells naturally competent

"The lake was isolated from the oceans about 3,500 years ago, when the continent lifted up around it." Is this a typo or is it somehow possible on such a time frame?

The action of the continental uplift was going on for a long time, but the lake was only cut off from the ocean at that point. It was a gradual process until the ocean just couldn't reach the lake anymore.

Lots of scientists say that if life can exist in extreme conditions then it must also exist on other planets with extreme conditions. I'm not sure about that. There is a key word in this text. Life ADAPTED. I'm pretty sure that once life is there at one moment, it will adapt to more extreme conditions, but it cannot be created in extreme conditions. We now know that there is life in places like that, but we have to prove how it can be created before assuming it can exist on other planets different than ours.

I agree what you said about "Life ADAPTED" and you also said "it cannot be created in extreme conditions". No argument there. Question is, when one says this is "extreme condition" for human species, but it may not be an "extreme condition" for other species because due to each of our own chemistry structures built differently. Some known microbes eat sulfur for lunch. Can we? Definitely not. Those stuff tastes awful. When you feed those sulfur eater microbes with spaghetti and meatballs, you might kill them instantly. So what is "extreme" to you and what is extreme conditions to the microbes? 1 million degree below C is extreme or 10 million degree below C is extreme, or 100 million F is extreme or 5,000 million F is extreme? So the problem is, there's no standardized ISO on such thing as "extreme".

Do you believe Mars is under such extreme conditions for all life? For human, may be. Who knows there might be some native born microbes over there don't think so. They are living quite comfortably.

What is the mechanism for a horizontal gene transfer between different species?

Does this transfer result in new species?

What is the normal method of reproduction? Is it sexual, asexual, either (depending on available mates)?

Does the gene transfer happen during reproduction or between two already living organisms?

How come none of these questions came up in the article?!?

As usual, reading Wheels of Confusion's post and following the link might help.

The organisms in this article are species of Archea, and are single celled organisms that reproduce asexually. As with many microorganisms, they are capable of exchanging DNA by conjugation <http://en.wikipedia.org/wiki/Bacterial_conjugation> and related mechanisms, in which organisms exchange DNA in a non-reproductive process.

The definition of "species" for prokaryotes is more a matter of opinion than a matter of concrete properties. The article states that the organisms are not all of one species, based on differences in the properties of he organisms. In general, horizontal gene transfer does not immediately result in formation of a new species, although it is one mechanism for speciation.

Kate Prengaman / Kate is a science and environmental reporter living in Yakima, Washington. She writes about everything from emerging energy technology to persistent environmental problems and she really likes plants.